This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to rotational movement of disc drive actuators.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative pneumatic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by flexures attached to the actuator.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. The actuator is mounted to the pivot shaft by precision ball bearing assemblies within a bearing housing. The actuator supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. These magnets are typically mounted to pole pieces which are held in positions vertically spaced from another by spacers at each of their ends.
On the side of the actuator bearing housing opposite to the coil, the actuator assembly typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. These actuator arms extend between the discs, where they support the head assemblies at their desired positions adjacent the disc surfaces. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved generally radially across the data tracks of the discs along an arcuate path.
As explained above, the actuator assembly typically includes an actuator body that pivots about a pivot mechanism disposed in a medial portion thereof. The function of the pivot mechanism is crucial in meeting performance requirements associated with the positioning of the actuator assembly. A typical pivot mechanism has two ball bearings with a stationary shaft attached to an inner race and a sleeve attached to an outer race. The sleeve is also secured within a bore in the actuator body. The stationary shaft typically is attached to the base deck and the top cover of the disc drive.
Bearing cartridges have been mounted within actuator bores in a variety of ways. Some have simply press-fit the cartridge into the bore; others have formed the bore of the actuator of plastic in order to facilitate such press-fitting. Still others have provided screws in the actuator body which extend into the bore, either to serve as set screws pressing against the cartridge sleeve or to engage threads in the cartridge sleeve so as to pull the cartridge into tight contact with the bore. However, all of these methods present additional problems: simple press-fitting risks damage to both the bore and cartridge; plastic bores are subject to thermal expansion and contraction, as well as fatigue; and providing screws and their bores requires additional parts, manufacturing steps and costs.
One solution to these problems has been to provide a groove in the outer surface of the sleeve, and then positioning a tolerance ring within the groove. The tolerance ring is typically made of a compressible yet resilient piece of material such as a corrugated steel sheet. The bearing cartridge and tolerance ring assembly is then press-fit into the bore of the actuator body, the tolerance ring holding the cartridge in place within the bore while yielding enough so that neither the cartridge nor the bore is damaged as a result of the press-fitting operation. This method has proven largely satisfactory.
However, even this arrangement raises other problems. The bearing and tolerance ring are typically made of steel because of its high strength. The actuator bore""s inner surface is typically made of aluminum because of its relatively low weight and cost. Aluminum is a much softer material than steel, so when the bearing cartridge and tolerance ring are pressed into the actuator bore, the steel corrugations tend to xe2x80x9cbitexe2x80x9d into the soft aluminum bore by mildly deforming the aluminum, resulting in a high level of friction between the ring and bore. Because the bearing cartridge is made of steel, however, there is little between the cartridge and ring to create friction between them. This greatly raises the risk of axial slippage between the bearing cartridge and the tolerance ring during shock events. In fact, tests have borne this out, indicating that slip between the ring and the cartridge occurs at about a mere 20% of the force required to cause slip between the ring and actuator bore.
In order to prevent slip between the cartridge and tolerance ring, then, it has generally been necessary to increase assembly forces to a very high degree. The result has been that slip between the cartridge and tolerance ring has been eliminated, by creating a tighter fit between the bore, ring and cartridge. The extremely tight fit has the added effects of making assembly more problematic, raising the risk of cartridge or actuator damage, and also results in frictional forces between the ring and bore far in excess of what is necessary to prevent slip between them.
What the prior art has been lacking is a bearing cartridge mounting arrangement which is easily assembled but which is resistant to slip when subject to axial forces.
The present invention is directed to an easily assembled bearing cartridge mounting arrangement. Prior to installing a bearing cartridge in an actuator bore, a tolerance ring is placed around the cartridge. The outer surface of the cartridge sleeve is provided with features which increase the frictional coefficient between the cartridge sleeve and the tolerance ring. The cartridge and ring are then press-fit into the actuator bore together. The increased friction between the cartridge and ring prevents slip between these two components, eliminating the need to increase compressive forces between the ring and the bore and bearing. Additional features and benefits will become apparent upon a review of the attached figures and the accompanying description.